1. Field of the invention
This invention relates generally to coated substrates and, in one particular embodiment, to a coated glass substrate particularly useful for the reflection of electromagnetic radiation, such as electromagnetic solar radiation.
2. Technical Considerations
With the increasing costs of fossil-based fuels, solar power is becoming a more commercially acceptable and economically viable source of energy. One known application is using mirrors to concentrate solar power for electrical generation. Mirrors having high reflectance of solar radiation are used for “concentrated solar thermal power” (CSTP) installations. There are several different mirror geometries used for these applications. One conventional system uses curved parabolic solar mirrors to concentrate solar energy onto tubes positioned along a focal line. A heat transfer medium in the tubes carries the absorbed heat energy to a generator station where it is used for power generation. Another conventional system uses a solar tower in which a number of flat solar mirrors direct solar energy at a particular location on the tower. The heat generated by the focused solar energy is transferred to a working fluid, such as sodium, and the heated working fluid is used for power generation.
Another application of such mirrors is for “concentrated photovoltaics” (CPV). In this application, mirrors focus or concentrate solar energy onto high-efficiency photovoltaic (PV) devices, thereby improving the energy output per device.
In these known systems, it is desirable that the mirrors reflect as much solar energy as possible. It is also desirable that the mirrors have as long a commercial life as possible to preclude frequent changing of the mirrors.
Conventional mirror technology utilizes a wet chemical application process in which silver is precipitated onto a glass substrate from a silver nitrate solution. A problem with this known system is that the spent solution must be disposed of in an environmentally friendly manner. Moreover, such conventional systems do not permit the coated article to be processed at high temperatures (e.g., for heat-strengthening, tempering or bending) after deposition of the silver layer because this will damage the silver layer. While some conventional mirrors have a wet-chemical applied copper layer over the silver layer to retard corrosion of the silver, these conventional copper layers cannot protect the silver layer sufficiently to allow the coated glass to be heated to its softening point. Further, the deposition of copper by wet chemistry is unattractive due to environmental reasons, particularly due to disposal of the wet chemical waste stream.
Therefore, it would be advantageous to provide a reflective article and a method of making a reflective article which eliminate or reduce at least some of the problems associated with such conventional articles.